A Kurdish peshmerga fighter looks at smoke rising in the distance following US air strikes on Islamic State militants at the Mosul dam, Iraq. Photograph: Ahmad al-Rubaye/AFP/Getty Images

US aircraft and drones continued to fly over the recaptured Mosul dam on Tuesday, after the Pentagon revealed just how much the bombing campaign had been intensified in the last few days to secure the complex.

The US military disclosed that more than half of the air strikes were launched to help recapture the dam from 500 Islamic State (Isis) militants. Since the start of aerial bombardment on 8 August, the US has launched 68 air strikes, including 35 to secure the Mosul dam in the last four days, Pentagon figures showed.

A Pentagon spokesman, Rear Adm John Kirby, said the Mosul dam air strikes had “destroyed over 90 targets including a range of vehicles, equipment and fighting positions”. The strikes helped Iraqi and Kurdish troops take full control of the dam on Monday.

Buoyed by the Mosul operation, Iraqi forces launched a new offensive on Tuesday to drive Isis fighters out of Saddam Hussein’s home town of Tikrit, 80 miles north of Baghdad.

“Our forces are advancing from two directions with a cover from army helicopters, mortar and artillery shelling the positions of the Islamic State fighters in and around the city,” an army major in the operations room told Reuters.

Barack Obama hailed the retaking of the Mosul dam as a symbol of how Isis militants could be defeated by co-operation between Kurdish, Iraqi and US forces. “This operation demonstrates that Iraqi and Kurdish forces are capable of working together and taking the fight to Isil [Islamic State]. If they continue to do so, they will have the strong support of the United States of America.”

But the size of the operation also revealed what it will take to defeat the insurgents. The analyst Elijah Magnier pointed out that it took just a day for Isis fighters to capture the dam earlier this month, but a week-long joint operation to take it back. “Urban warfare is different,” he warned.